The simian retroviruses simian T-lymphotropic virus I, simian immunodeficiency virus, and type D retrovirus are important animal models for the study of human immunodeficiency and also pose a threat to the health of captive domestic breeding colonies. Herpesvirus simiae is a proven hazard to animal care workers and laboratory personnel. New England Regional Primate Research Center (NERPRC) has successfully established a specific-pathogen-free (SPF) rhesus monkey breeding colony to provide uninfected experimental subjects and to improve colony health. We propose to expand the colony to 250 monkeys in support of these crucial goals. The breeding colony will be self-sustaining and provide 35 SPF rhesus monkeys annually for the ongoing and Federally funded research programs at the NERPRC. Uninfected animals will be identified using proven serologic and virus isolation techniques. SPF animals will be group housed in a dedicated modern concrete block building. The SPF status of the colony will be ensured through periodic serologic surveillance. The genetic diversity of the breeding colony will be maximized by tracking of individual animal pedigrees to avoid inbreeding and by periodic determination of average heterozygosity through analysis blood protein polymorphism. Behavioral management and study will ensure that SPF breeders have normal social and maternal characteristics.